1. Field of the Invention
The present invention relates to a suspension system for a vehicle and, more particularly, to a suspension system which can enhance running safety, cornering safety and ride comfort by optimally controlling the change of a camber in accordance with the vehicle's travelling conditions.
2. Description of Related Art
In general, a vehicle suspension connects an axle shaft and a vehicle body to each other and absorbs impact and vibration from a road surface to increase riding comfort and running safety. To absorb the impact from the road surface, a connection of upper and lower parts of the suspension should be flexible, and to cope with driving and breaking forces applied to a wheel and a centrifugal force in a vehicle's turning, a connection in the horizontal direction of the suspension should be durable.
The suspension system is structurally characterized as an integral shaft suspension and an independent suspension. The suspension of the present invention concerns an independent suspension. There are MacPherson strut type suspensions and Wishbone type suspension systems in the suspension systems.
As shown in FIG. 5, the conventional MacPherson strut type suspension system comprises a strut assembly 55, a shock absorbing means, consisting of a shock absorber 51 and a spring 52 and having a lower end fixed to a wheel carrier 53 pivotally supporting a wheel 50 and an upper end supportably connected with a vehicle body 54; and a lower arm 56 connecting a lower side of the wheel carrier 53 to a lower side of the vehicle body 54.
A section of the wheel's up-and-down movement is determined by the lower arm 56 during a wheel's up-and-down vibration. The vibration is absorbed by an elastic bushing 57 of the vehicle body-side connecting portion of the lower arm. The impact from the road surface is absorbed by the shock absorber 51 and spring 52 of the strut assembly 55.
However, considering the operational steps of the above-described suspension system, when the wheel vibrates upward and downward in accordance with travelling conditions, the wheel moves upward and downward by a predetermined length of the lower arm. Thus, the wheel moves upward and downward according to a tracing movement M which is formed by the length of the lower arm and the sliding movement of the strut arm. The camber angle is changed according to the wheel's up-and-down movement and has a great effect on ride comfort, cornering safety, and running stability.
That is to say, since the wheel side end connection portion of the lower arm 56 is designed to be disposed at the lower side of the wheel center, when the wheel moves upward along the tracing movement M in a normal ascending section, the lower side of the wheel is pushed outward along the curvature of the tracing movement M, whereby the wheel is changed to a negative (-) camber.
However, in the section over the normal ascending section, that is, after the wheel 50 passes a predetermined height, the lower arm 56 ascends while pulling the lower side of the wheel according to its tracing movement, such that the camber angle of the wheel is changed again to a positive (+) camber.
The change of the camber as described above is illustrated by the broken line of FIG. 4A which will be described in detail in the description of the invention. Further, the tread is changed as illustrated by the broken line of FIG. 4B by a change in the camber, whereby the steering characteristics and running stability are adversely affected.